This invention relates to programmable logic devices, and more particularly to providing programmable logic devices with content addressable memory capabilities.
Heile U.S. patent application Ser. No. 09/034,050, filed Mar. 3, 1998 (which is hereby incorporated by reference herein in its entirety), shows that programmable logic array integrated circuit devices that have large blocks of random access memory ("RAM") (or read-only memory ("ROM")) can be equipped to facilitate the performance of product term ("p-term") logic in the RAM (or ROM). (For convenience herein, the ROM alternative will be understood to be included in references to RAM.) As the immediately above-mentioned reference explains, the ability to perform p-term logic in large blocks of RAM on a programmable logic device that may also include other types of programmable logic capability (e.g., large numbers of small, programmable, look-up tables for performing look-up table logic) increases the flexibility and usability of the device.
There are also applications of programmable logic devices that would benefit from having content addressable memory capability on the devices. A content addressable memory is one in which different "words" of data are stored in different word locations in the memory, and when data matching one of the stored words is applied to the memory, the memory responds by outputting an indication of the location found to contain the applied data. Content addressable memories ("CAMs") are also sometimes called associative memories.
In view of the foregoing, it is an object of this invention to provide programmable logic devices with improved content addressable memory capabilities.
It is another object of this invention to provide programmable logic devices with content addressable memories, the contents of which can be efficiently changed during operation of the device.